Building Cadence.....

[Yelsel]

I would love to hear what KnottedYet has to say about this... poking about with actual muscle fibers is awesome!

But I think people are overestimating the importance of muscle twitch fibers. Most people are born with about a 50/50 ratio; it is the top-level athletes that have very skewed proportions... up to 80/20.

There is actually a whole gradation of muscle fiber types... but these are lumped into slow twitch and fast twitch, with a further split in fast twitch. As might be expected by the names... fast twitch contract rapidly, slow twitch more a slow and steady ratcheting. If you pick up a baby, that is fast twitch. Holding the baby is slow twitch.

I - slow twitch fibers -- exclusively aerobic, need oxygen. Endurance fibers.
IIa - fast twitch a -- use both aerobic and anaerobic pathways equally well, but still contract rapidly.
IIb - fast twitch b -- use anaerobic pathways (no oxygen) exclusively; best for short sprints. In the 50 to 100 yard dash, athletes do not need to breathe at all, and some don't!

The IIa is where it gets interesting. You can train these muscle fibers to be more efficient at aerobic use -- by increasing the number of mitochondria (and in general increasing number of capillaries to the muscle). Mitochondria are the "powerhouses" of the cell, where glycogen (glucose molecules) is turned into ATP (adenosine triphosphate - the typical energy "currency" of the cell.) IIa fibers are also sometimes called "switch" fibers because depending on training, you can run these fibers equally well with oxygen or without. So IIa fibers will still contract rapidly, but you can use them much longer without fatigue, since you are using the aerobic pathway. Another way of stating this: if you are training to raise your lactate threshold, you are training your IIa fibers to better utilize oxygen / use the aerobic pathway.

I suspect that cadence is going to be a function of a lot of the body's systems, not just muscle fiber ratios... while they are individual at a fine scale for each person (by both nature and nurture), for the "average" person the ratios are roughly the same. (Though one can argue whether even non-competitive people self-selecting for a sport, or even interested in sports at all, are "average"!).

VO2 max -- the body's ability to utilize oxygen -- is another important factor. I suspect this might even be more important than actual muscle fiber composition for cadence... Lance Armstrong has an extremely high VO2 max, the highest in cycling and as high as most competitive Nordic skiiers (which requires the most oxygen use) -- 81 mL / m / kg (Utilizes 81 milliliters of oxygen per minute, per kilogram of body weight). Women have a lower VO2 max then men; the top women skiiers are typically in the high 70s. This is partly due to typically lower lean mass and higher body fat percentage; even correcting for kg of lean body mass (or just muscle mass), women are still lower. This is likely because our hearts are smaller and even at their most efficient will have a lower stoke volume (amount of blood transported in one heartbeat).

There is a genetic ceiling for each person with respect to max VO2, though unless you are a competitive athlete with serious training, we don't usually reach this. (The ability to rapidly increase max VO2 is partly genetic and partly training type, which is why an experienced coach is invaluable at helping to efficiently train to your genetic potential; in comparison training to raise lactate threshold is fairly standard.) As far as the limiting factors on utilizing oxygen, there is a debate about oxygen transport (cardiovascular system) vs. utilization (ability of mitochondria to use delivered oxygen). I fall on the side of transport limitations, because heuristically it makes sense that women's VO2 max is lower (scaled by muscle mass) because our heart and blood volume is proportionally less than in men, rather than we suck at growing capillaries and mitochondria, which should not be gender specific!

As a side note: the limiting factor is *not* lung capacity or oxygen-carbon dioxide gas exchange in the lungs; sedentary asthmatics are limited by these, but 4-6 weeks of 1 hour low-intensity exercise 5x/week or 30 minutes of moderate-intense activity 3x/week will increase VO2 max to equal that of a control group. This is because asthmatics can rapidly increase lung capacity through exercise (gas exchange efficiency is only slowly or not reversible, since it involves scarring in the lungs... as an asthmatic, I am happy that it is not a limiting factor though!). Exercise does not reduce intensity or severity of asthmatic reactions, which was originally a hope. But it does rapidly lead to a better quality of life after a short period of discomfort.

Heart rate and stoke volume (pumping volume) are part of the VO2 max metric. Raising lactate threshold (essentially the body's capacity to utilize oxygen / run systems aerobically) is part of training the "switch" IIa fast fibers to better utilize oxygen. As a cyclist improves max VO2 and raises her lactate threshold, she will generate more power, and should be more comfortable in a higher cadence if she trains that way. (It is also quite possible to generate more force at lower cadences... I really don't have a sense of how much influence Lance's fast spinning has as a cycling trend, vs. how much it is always more efficient to have a fast cadence. Michael Phelps' swimming style does seem to be a genuine innovation worthy of emulating in swimming; I really don't have a sense of how important Lance's fast cadence is to cycling. Guess I should finish the books on cycling physics. ) Muscle fatigue should be lower for higher cadences... which would be opposite as far as distance cycling = slow twitch fibers if high cadences = fast twitch fibers (lower fatigue / longer distances). Maybe that is part of the equalizing factor leading to a wide range of people cycling?

One last comment: muscle strength depends on a lot of factors; it is possible to significantly increase muscle strength, at least up to a point, without increasing muscle *size* - hypertrophy. One of the biggest limiting factors in strength is actually tendon and bone strength (there is a "tension meter," the golgi apparatus, built in to every tendon to help your brain limit your muscle fibers to acceptable rate / force of contraction -- in times of great stress, such as lifting a car from a spouse, your brain will override this tension limitation, though it really messes up your muscles / tendons / ligaments / bones.) Conversely, you can build up size without increasing functional strength that much (extreme bodybuilding / muscle isolation is the culprit in this!). Hypertrophy = increasing muscle fiber thickness; this happens almost exclusively in fast twitch fibers. Some animals also produce new muscle fibers; but either humans do not, or do it so slowly the effect is negligible.

@Oakleaf -- I'll take up more on heartrate later in a new thread. The short answer is that the Garmin is just using a formula 220-age if you do not set your max heart rate manually; so you haven't necessarily dropped your max heart rate. Your Garmin has no clue what your maximum heart rate actually is, and is just merrily assigning you one and decreasing it every year by rote.